While lifespans are increasing, so is age-related loss of cardiovascular, immune and cognitive functions. It is necessary to better understand the biology of healthy aging that focuses on increasing the number of years one remains healthy and free of age-related disorders. These years, termed health span, often associate with the ability to maintain youthful stress response, motor function, and cognition. This project examines the role of a bioactive lipid pathway ? sphingolipid metabolism ? on increasing health span. For this, we analyze lifespan, oxidative stress, and locomotor function using the model organism C. elegans. First, this project examines whether reducing mRNA expression of sphingolipid enzymes, specifically at older ages, affects lifespan, survival to oxidative stressors, and neuromuscular function. We use physiological and cellular experiments, RNA interference, and gene expression analyses to examine a panel of sphingolipid genes. In particular, the proposal examines whether one sphingolipid, sphingosine- 1-phosphate (S1P), can promote improved health span and whether another, ceramide, worsens healthspan. Secondly, the project examines how sphingolipids mediate bacteria-host interactions, specifically to modulate innate immune responses. For this, we determine whether mutations in sphingolipid genes affect the induction of innate immunity signaling pathways following stress. We also examine the gene expression of sphingolipid metabolism enzymes and sphingolipid content in known aging mutant models, including the insulin signaling, dietary restriction, and mitochondrial respiration pathways. In addition, we analyze bacterial gene expression in these models of aging, to elucidate how microbial gene expression dynamics differ in aging hosts. Sphingolipids are major players in the intestinal tract and function in stress response; using mutants with altered sphingolipid signaling, gene expression analysis of sphingolipid enzymes, and bacterial transcriptomics, we might gain insight into how sphingolipids mediate stress responses and host physiology during aging. Together, the project aims to generate invaluable datasets that interrelates host sphingolipids, the gut microbiome, and age to identify novel players in promoting healthy aging.